Just one month after announcing free voice calls over Wi-Fi in BlackBerry Messenger, Research In Motion delivers the feature to all handsets running BB 6 OS or better. A video demo shows the added functionality, which could save money for some, easy to use.

The new feature should be especially useful in areas with high wireless network concentration and in regions where voice calling minutes are still expensive. While handy in the U.S., for example, voice over Wi-Fi is likely to appeal in areas where the BlackBerry brand is still strong: Emerging markets that don’t yet have cheap voice minutes over cellular or are limited by cellular network coverage.

A video demonstration made by Research In Motion illustrates the seamless experience of starting a voice call from a message thread. One button tap initiates the call, keeping the message stream open for IMs or photo sharing.

Research In Motion says the updated BBM 7 client is supported on handsets running the BlackBerry 6 OS software now, with anticipated support for older devices running BB 5 OS early next year.